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OK, this is a trick question -- 'SOS' doesn't stand for anything at all. Learn the history of these three terms, including what astronomy and telegraphy have to do with it, in today's episode of BrainStuff, based on this article: https://people.howstuffworks.com/am-pm.htm; https://people.howstuffworks.com/what-does-sos-mean.htm
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